styled the menu button

css/area_header.less

@@ -3,3 +3,45 @@
  *
  * @author Jana Deutschlaender <deutschlaender@cosmocode.de>
  */
+#dokuwiki__header {
+
+    .menu-togglelink {
+        border: 1px solid @color-border;
+        border-radius: @border-radius;
+        text-align: center;
+        margin: @very-small-spacing -(@very-small-spacing) 0 0;
+
+        font-size: @font-size-small;
+        min-height: 2em;
+        min-width: 2em;
+        box-sizing: border-box;
+        line-height: 2em;
+
+        cursor: pointer;
+        background-color: #fff;
+        text-decoration: none;
+        transition: @transition color, @transition background-color, @transition border-color;
+
+
+        svg {
+            height: @font-size-default + (@font-scale-factor * 4);
+            width: @font-size-default + (@font-scale-factor * 4);
+            vertical-align: middle;
+            path {
+                fill: @color-nav
+            }
+        }
+
+        &:hover,
+        &:active,
+        &:focus {
+            background-color: @button_color;
+            border-color: @button_background;
+            svg path {
+                fill: @button_background;
+            }
+        }
+
+    }
+
+}

css/base_structure.less

@@ -153,6 +153,8 @@
                 }
             }
         }
+
+
     }
 
     .showSidebar {

img/menu.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24"><path d="M3 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2z"/></svg>

tpl/main-sidebar-logo.php

@@ -1,9 +1,14 @@
 <?php
-    if (!defined('DOKU_INC')) die();
+if(!defined('DOKU_INC')) die();
 
-    echo '<div class="menu-togglelink mobile-only"><a href=\'#\'>MOB</a></div>';
-    echo '<div class="logo">';
+echo '<div class="menu-togglelink mobile-only">';
+echo '<a href="#">';
+echo inlineSVG(__DIR__ . '/../img/menu.svg');
+echo '<span class="sr-out">'.tpl_getLang('a11y_sidebartoggle').'</span>';
+echo '</a>';
+echo '</div>';
 
-    \dokuwiki\template\sprintdoc\Template::getInstance()->mainLogo();
-
-    echo "<hr class=\"structure\" /></div>";
+echo '<div class="logo">';
+\dokuwiki\template\sprintdoc\Template::getInstance()->mainLogo();
+echo '<hr class="structure" />';
+echo '</div>';